1. Field of the Invention
The present invention relates to a coating composition whose main component is a polyamide resin (hereinafter referred to as "nylon" (trademark) and into which charcoal powder is composed. The composition is used as a material for an architecture, especially as a coating for an interior wall, an underfloor lining, a back lining of a ceiling and a closet.
2. Related Arts
An ordinary house, whether of a reinforced concrete or of wood, tends to be highly moist at a poorly ventilated part, undergoing a dewing and an associated early damage. To avoid this, a desiccant or a heat insulating material is placed or an air conditioning machine is installed.
However, a desiccant serves only to absorb moisture and becomes saturated soon, and thus requires to be replaced frequently. Furthermore, high moisture poses a further effort to combat with molds and hazardous insects.
Now, charcoal absorbs moisture when the atmospheric humidity becomes high, while releases moisture when the humidity becomes low, whereby exerting an ability of keeping the moisture content at about 55% in average, which is called a humidity-controlling effect.
In addition to the utility as a solid fuel, the charcoal shows an effect for keeping off mold, a pesticidal effect for combating with mites and termites and a deodorizing effect for adsorbing unpleasant odors such as ammonia and formaldehyde. Other various excellent properties of the charcoal were also found recently, such as an ability of attenuating electromagnetic waves generated from electrical appliances for domestic use and an air-cleaning effect which allows the negative ion level to be increased while capturing positive ions in the air, thus a wide-range application of the charcoal for the purpose of improving human health and living environment is investigated.
Accordingly, I considered that a building coating having an excellent property of charcoal can be obtained by mixing charcoal powder with a base coating of a synthetic resin and a solvent therefor, and then made an attempt to develop a coating containing charcoal powder.
The charcoal is a black porous material obtained by heating a wood such as evergreen oak or Japanese oak under reflux in the absence of air, and classified broadly into white charcoal with whity surface and black charcoal depending on difference mainly in the manufacturing process. A representative white charcoal is bincho charcoal originated from a raw lumber of holm oak, which is obtained by burning a wood at a temperature as high as 900 to 1400.degree. C. and then pouring a mixture of a suitable amount of water, ash and soil onto the wood taken out from a furnace, whereby effecting a rapid cooling. On the other hand, black charcoal is obtained by burning miscellaneous woods including Japanese oak or other oaks at a temperature of 600 to 800.degree. C., allowing to cool, and then taking them out of the furnace.
Since the charcoal has a microporous structure in its nature, it can readily be pulverized into microparticles having a size of 10 to 30 .mu.m. In order to prepare a coating containing such charcoal microparticles, various resins, solvents and vehicles are admixed and a test for evaluating the practical utility was performed, and the results obtained were poor in general, because of a poor solubility in a solvent intrinsic to the charcoal. Thus, charcoal powder was attempted to be incorporated into various solvent-based coatings and water-based coatings, but a feasible coating could not be obtained, because of the problems such as difficulty in dispersing uniformly in a mixing step as well as an uneven color in a practical painting step.